Variations in how much fluid is present in a person's thorax can take various forms and can have different causes. For example, eating salty foods can result in retaining excessive fluid in the thorax, which is commonly referred to as “thoracic fluid,” and elsewhere. Posture changes can also affect the amount of thoracic fluid present at a given time. For example, moving from a supine to standing position can shift intravascular fluid away from the thorax, toward the lower extremities.
Another cause of fluid build-up in a person's thorax is pulmonary edema, which involves buildup of extravascular fluid in the lungs. In pulmonary edema, fluid accumulates in extracellular spaces, such as the spaces between lung tissue cells. One cause of pulmonary edema is congestive heart failure (CHF), which is also sometimes referred to as “chronic heart failure” or simply as “heart failure.” In many situations, CHF can be conceptualized as an enlarged weakened portion of heart muscle. The impaired heart muscle results in poor cardiac output of blood. As a result of the impaired heart muscle, fluid tends to pool in blood vessels in the lungs and becomes a barrier to normal oxygen exchange. This intravascular fluid buildup, in turn, results in the extravascular fluid buildup mentioned above. Accordingly, pulmonary edema may be an indicative and important condition associated with CHF.
Yet another example of thoracic fluid accumulation is pleural effusion, which is the buildup of extravascular fluid in the space between the lungs and the rib cage. The lungs are covered by a membrane called the pleura, which has two layers, an inner layer and an outer layer. The outer layer lines the rib cage and diaphragm. The inner layer covers the lungs. The pleura produces a fluid, which acts as a lubricant to help in breathing, allowing the lungs to move in and out smoothly. Pleural effusion is the accumulation of too much of such fluid. Pleural effusion, like pulmonary edema, may also result from CHF and provide an (early) indication that heart failure is present or has worsened.